In x-ray imaging, for instance in computed tomography, angiography or radiography, counting direct-conversion x-ray detectors or integrated indirect-conversion x-ray detectors can be used.
The x-ray radiation or the photons can be converted in direct-conversion x-ray detectors by a suitable converter material into electric pulses. CdTe, CZT, CdZnTeSe, CdTeSe, CdMnTe, InP, TlBr2, HgI2, GaAs or others can be used as the converter material, for example. The electric pulses are evaluated by an evaluating electronic system, for example an integrated circuit (Application Specific Integrated Circuit, ASIC). In counting x-ray detectors, incident x-ray radiation is measured by counting the electric pulses which are triggered by the absorption of x-ray photons in the converter material. The level of the electric pulse is generally proportional to the energy of the absorbed x-ray photon. By this means, spectral information can be extracted by comparing the level of the electric pulse with a threshold value.
The x-ray radiation or the photons can be converted in indirect-conversion x-ray detectors by a suitable converter material into light and via photodiodes into electric pulses. Scintillators, for instance GOS (Gd2O2S), CsJ, YGO or LuTAG, are frequently used as converter material. Scintillators are used particularly in medical x-ray imaging in the energy range up to 1 MeV. What are known as indirect-conversion x-ray detectors, known as scintillator detectors, are typically used, in which the conversion of the x-ray or gamma radiation into electric signals takes place in two stages. In a first stage, the x-ray or gamma quanta are absorbed in a scintillator element and converted into optically visible light; this effect is referred to as luminescence. The light excited by luminescence is then converted in a second stage by a first photodiode, which is optically coupled to the scintillator element, into an electric signal, read out by way of an evaluation or read-out electronics system and then forwarded to an arithmetic unit.
In a detector apparatus for computed tomography systems, data from many x-ray detectors is routed to a central data interface. The data is forwarded from this data interface via a slip ring transmission system to an arithmetic unit. For instance, the data can be retrieved from the individual x-ray detectors via a controller, stored in an intermediate unit, sorted and then sent to the arithmetic unit.